The respiratory protein in marine worms is termed hemerythrin. In the coelomic fluid it is an octamer and in the retractor muscle it is a monomer. These forms from the species Phascolopsis gouldii (East Coast) and Themiste pyroides (West Coast) will be examined. The kinetics of the important physiological reactions namely a. oxygenation of deoxyhemerythrin b. autoxidation of oxyhemerythrin and c. reduction of methemerythrin will be investigated by rapid reaction techniques. A comparison of the behavior of the different polymeric forms and from different species will be made for the first time. A comparison of these reactions with the corresponding ones of myoglobin and hemoglobin, the important mammalian respiratory proteins will be made.